In a field effect transistor comprising a support substrate, and a gate electrode and a semiconductor portion separated by a gate insulation portion, a source electrode and a drain electrode provided so as to contact the semiconductor portion formed on the support substrate, an organic material is used for the semiconductor portion. The organic material attracts attention because the semiconductor portion can be formed by application of its solution, and weight reduction can be achieved and impact strength can be imparted by use of e.g. a polymer, in addition to advantage in view of cost over a conventional formation process by e.g. vacuum process employing an inorganic material such as a silicon.
However, a device employing an organic semiconductor has been known to be generally poor in driving stability as compared with an inorganic semiconductor device. As one item representing the driving stability, a shift in the threshold voltage may be mentioned. That is, the threshold voltage changes by a stress by application of a gate voltage. In a case of an inorganic semiconductor material, a shift in the threshold voltage within 3 V is considered to be tolerable in view of practicability within the life of a display device which is a typical application of the field effect transistor. However, in a case of a field effect transistor employing an organic material such as pentacene or a polyfluorene polymer for the semiconductor, the shift in the threshold voltage is significant, such being practically problematic (Non-Patent Documents 1 to 3).
Further, Non-Patent Document 4 proposes a process of forming an organic semiconductor layer by applying a pentacene precursor solution, followed by conversion into pentacene. However, according to studies by the present inventors, in a field effect transistor to be produced by the proposed process, the mobility of the semiconductor layer is at a level of 089 cm2/(V·s).
Non-Patent Document 1: Journal of Applied Physics, 2003, Vol. 93, p. 347-354
Non-Patent Document 2 Physical Review 3, 2003, Vol. 68, No. 085316
Non-Patent Document 3: Applied Physics Letters, Vol. 79, No. 8, p. 1124-1125
Non-Patent Document 4: Journal of American Chemical Society, 2002, Vol. 124, p. 8812-8813